4wd low problem

[coppertahoe]

Hey everyone, so my truck has the push button 4wd, and anyways I can go into 4wd hi no problem. But when I try to go into low, the light flashes likes its about to work, but it just wont engage. My mechanic said it was a sensor. Maybe a speed sensor or something? I know your supposed to be moving in neutral when going into 4low, so some sort of speed sensor makes sense to me. But what do I know

 

[SunlitComet]

You can do it in plain neutral really. At any rate when it go into 4lo you will hear and feel it as it really stands out. Do you hear or feel anything when switching?